Bill Edwards on tue 16 dec 03
The archives is loaded with this information and goes
way back on Chromium. But lets look at the other side
of the coin as well. All oxides/colorants are within
the ranks of chromium as far as something burning out
during firing based on maximum combustion levels. Each
will come with its own special set of rules or
problems and thats where we try and learn NOT to
breath the fumes as potters or suck in the dusts as
potters since we are the one who would most likely be
exposed to it. Chromium is in plants and foods as well
as copper and many other life giving nutrients.
Scientifically too high a level of most anything can
become toxic at some level to all or part of the body
based on entry, esposure and contaminate.
The Reference Dose (RfD) for trivalent chromium is 1
mg/kg/day. This level is more than 300-fold the upper
limit of the ESADDI, making trivalent chromium one of
the least toxic nutrients.
http://www.nutrition.org/nutinfo/content/chro.shtml
http://www.epa.gov/safewater/contaminants/dw_contamfs/chromium.html
It is important to know what places us in jeopardy but
the list is so vast and the unknown factors of
exposure is totally a ball game even for toxicoligist.
Exposure may come from something that was present via
industry years ago and still lingering somewhere in
the background. We can't solve that here! They are
still finding high levels of lead from old paint
scrapings under the rails and bridges in NY and other
places. Pinking is not a sign of anything other than a
loss of some gasses that are inherently attracted to
tin molecules very similar to carbon or reduction that
changes copper to red or copper to a matallic in raku
which is something we try to shoot for in that firing
fashion.
If its the pinking issue thats the problem, if you see
it, it has to be a killer glaze thing, then try
this... Reduce the calcium by subbing strontium in as
a partial replacement for the calcium. Its also known
that MgO mixed in with strontium as a partial
replacement will also help. Using a straight strontium
sub most likely won't let you achieve the goal unless
its just the white your after and for whatever reason
your kiln is still providing you a slight pink tint to
the white your using after a couple firings.
Exhausting the kiln during operation is advised to
help move the residual fuming though the system and
hopefully a shorter purge so that the next Tin white
glaze you use comes out like snow. Lowering the
calcium in a white glaze and upping the AL203 closer
to 3 and Silica to 3 +/- (^6 ox) a small amount and
using wollastonite can help produce and much more
suitable tin white that doesn't have the affinity for
pinking as much as the tins with high calcium and
lower AL203. I would read this on Wollastonite while
web browsing, consider the low melting point eutectics
as you read about this wonderful material.
http://www.nycominerals.com/cache/page_1048-1051.html
The MCL or Maximum Contaminate Level for Chromium
(ALL) in drinking water is 0.01 PPM or parts per
million. In lab results where I purposely have had
leachate/extraction testing done on chrome tin and Tin
White Pinking the levels were very much lower on the
actual piece and easily would pass muster based on the
recipes I use with levels exremely lower than the
recommended contaminate information available today.
Of course it would be. So apparently its the fumes
that seems to be the issue and chromium we use is 3
not 6 and there is a BIG difference in these animals.
A link to all the Chromium information you can stand
in one setting.
http://www.greatdreams.com/chrm6.htm
I would like to think that no one stands around the
kiln during firing or in locked rooms without
ventilation no matter what you are firing since clay
fired to bisque carries its own set of problems as
well as does any materials during combustion. We use
materials as potters as safely as possible and of
course finding an unknown danger and alerting people
would be benificial, but this has been covered to the
9th degree (see archives) and still no one has decided
a clear cut answer. Its just a stand off of
differences in what one percieves as a danger, another
see's it scientifically safe and usuable. I personally
will use chromium and will use common sense and do the
right thing and not inhale anything coming from the
kiln or be kicking up dust where I work no more than I
just have to. The rest is business sense! I would say
the same for any dust, its all hazardous not
neccessarily toxic.
Bill Edwards
=====
http://www.geocities.com/tallapoosarivergallery/index.html (Coming soon)
http://www.tallapoosariverpottery.com/
"Anyone whose panties get in a bunch over what I have to say from my
tiny corner oughta order some bigger roomier panties....!"
Bill Edwards
PO Box 367
Camp Hill, Alabama. 36850
__________________________________
Do you Yahoo!?
New Yahoo! Photos - easier uploading and sharing.
http://photos.yahoo.com/
iandol on thu 18 dec 03
Dear Bill Edwards,
Thank you for that well argued essay on Chrome and other delights.
So, what is the pink colour. Is it Stannous Chromate?
Best regards,
Ivor Lewis. Redhill, South Australia
| |
|
